Using a PV cell to charge NiCd etc

Happy Hunter · Post by **Happy Hunter** » 11 Jul 2005, 15:38

Following on from another thread about charging a 12v car battery, I'm interested in known what kit I would need to charge NiCds?

I've got a 12V 1.8 W 'battery saver' PV cell like this one:
http://www.maplin.co.uk/Module.aspx?Mod ... 4&doy=11m7

Do I use a charge controller to bring the V down? I'm asuming this allows you to set a voltage you want and it regulates the output?

I've got a device that needs 6.4v and 250mA to charge (coming normally from a mains charger) but I guess as long as the V is correct the A can be less that required and it will just take longer? But not more or it could damage the batteries?

do I just work it out using P = V x A

thanks

fishertrop · Post by **fishertrop** » 16 Jul 2005, 20:58

Putting together something that charges nicads can be useful in a number of ways.

With one of those 12v PV panels, you have a number of choices:
1) Buy a battery charger that can take 12v as an input, such as:
http://www.argos.co.uk/webapp/wcs/store ... from=image
2) Charge a 12v battery and do the same as above (better for cloudy days or where your PV panel can't produce the required power)
3) Reduce the voltage with something like:
http://www.maplin.co.uk/Module.aspx?Mod ... 3&doy=16m7
4) Charge a 12v battery and use a mains inverter to run a regular 240v charger

I also like units such as these:
http://www.maplin.co.uk/Module.aspx?Mod ... 8&doy=16m7
which are a doddle to use and can just sit on your window sill all day doing the work

Rechargable batteries, esp NiMh types, work best and last longest when charged at a specific voltage + current for a specific time - you generally don't get this with home-made and (sun-variable) direct PV systems.

PV "charge controllers" generally take power from PV panels and regulate it to level best sutied to charge 12v batteries, so usually they take in 12v-15v and set the output at approx 12.8v or such (with current regulation also). You can pay as much as you like for high-end charge controllers and whilst this makes sense on a big 12v home-power system I think such units are probably not best suited for a nicad project.

Running a regular battery charger that takes 6.4v from a transformer at anything other than 6.4v will likely wreck the charger, not the batteries

AllanH · Post by **AllanH** » 24 Nov 2005, 09:05

Hi,

I'm looking to get a NiMh solar battery recharger. I've seen a few that look good but most can't handle 9v batteries (PP3). I think I'd need one that can handle these if power went off for a good while as I can plug 4 together to give 36v output. Does anyone know of a good charger that can do 9v & if so how long it takes, can it charge the other lower voltage batteries too.

The only one I've seen is

http://amail.co.uk/cgi-bin/e-buy.pl?dom ... ATTCHARGER

Anyone know if this is any good or if there are any better ones?

I also liked the look of the universal solar battery charger at http://www.cat.org.uk/shopping/search.t ... 0&reinit=1
Would it be possible to get this to charge 9v batteries too (eg attaching clip on 9v attachments to the other terminals - I'm not too technical so I'd be taking a bit of a risk).

Thanks

AllanH

revdode · Post by **revdode** » 24 Nov 2005, 10:09

The first charger should work although it looks like a prety basic charger from the price and sketchy details. Using this form of charging from solar with Nimh batteries is a concern. It's difficult to gauge how long to charge a battery based on the power supplied, these simple chargers from the mains usually have a timer or time table for charging. I was concerned about what this kind of uneven charging might do to battery life so went for a small panel charging a 12V battery through a simpe charge controller, this then feeds a smart charger which should I hope extend the life of the batteries I use. The charger I use also supports PP3 batteries, it is intended for use in cars from ebay.

AllanH · Post by **AllanH** » 24 Nov 2005, 12:52

Revdode wrote:

went for a small panel charging a 12V battery through a simpe charge controller, this then feeds a smart charger which should I hope extend the life of the batteries I use. The charger I use also supports PP3 batteries

If I understand right you're charging a 12v battery then just using it to charge smaller batteries. How long does it take, both to charge the 12v & to charge others from it? I assume you can only charge the 1 9V from the 12v?
Is the charger you use for the smaller batteries just a mains charger but getting power from 12V?
Could you give an idea of how much this settup cost as it seems to give greater flexibility than the standard battery charger I posted (if you know the name/have a site address for the supplier I'll take a look myself.

Thanks

AllanH[/quote]

revdode · Post by **revdode** » 25 Nov 2005, 13:04

AllanH wrote: If I understand right you're charging a 12v battery then just using it to charge smaller batteries. How long does it take, both to charge the 12v & to charge others from it? I assume you can only charge the 1 9V from the 12v?
Is the charger you use for the smaller batteries just a mains charger but getting power from 12V?
Could you give an idea of how much this settup cost as it seems to give greater flexibility than the standard battery charger I posted (if you know the name/have a site address for the supplier I'll take a look myself.

That pretty much sums it up.

It didn't really come from one supplier, the 12V battery is part of a portable charger cell (lidl), I use a 15W solar panel bought on ebay, the charge controller was built to a circuit found on a homebrew solar website although Maplin sell them for around a tenner, better ones are available on ebay for less. The charger is either from maplin or ebay, not quite sure which as I seem to have accumulated a lot of different chargers since I started using rechargeable batteries. It is intended to charge from the 12V supply in a car and complete with a cable and plug for a car power / lighter adapter.
The total cost wasn't high and it's more toy / experiment than practical application of PV, It probably cost me under ?50 total plus some time for tinkering. I don't charge batteries all the time so it's difficult to gauge charge times. I tend to leave it alone for a day in summer to recover if I drain it, in winter this takes most of a week, more if as now it has a dusting of snow:)

Things to do to improve this - at least one more panel - although these aren't as cheap and easy to find on ebay now, better battery (deep cycle) and fit a bought charge controller. Mount the panel(s) on the roof to keep it in full sun all day.

One way to save cash would be to drop the charge controller this risks ruining the battery - not likely with a 15w panel and saves a little loss (a few mA).